With the aid of such a governor it is possible to drive a dynamo from a mill shaft providing the requisite power, but of which the speed of rotation is not sufficiently uniform to secure alone efficient regulation of electromotive force.  Another device, patented by Mr. Crompton, is a modification of that method of field magnet winding commonly known as compound winding.  The field magnets are wound over with two wires, one of which has a high resistance and is arranged as a shunt, and the other of which has a low resistance and is arranged in series.  Instead, however, of the magnetizing powers of these coils being united in the same direction as an ordinary compound winding, they are opposed to one another.  That is to say, the current in the shunt wire tends to magnetize the iron of the field magnets in an opposite direction to that of the series wire.  It results from this that any slight increase of speed diminishes the strength of the magnetic field, and vice versa.  Accordingly, within certain limits, the electromotive force of the dynamo is independent of the speed of rotation.

* * * * *

THE ELECTRIC CURRENT AS A MEANS OF INCREASING THE TRACTIVE ADHESION OF RAILWAY MOTORS AND OTHER ROLLING CONTACTS.[1]

  [Footnote 1:  Read before the American Association for the
  Advancement of Science.  New York meeting, 1887.]

By ELIAS E. RIES.

The object of this paper is to lay before you the results of some recent experiments in a comparatively new field of operation, but one that, judging from the results already attained, is destined to become of great importance and value in its practical application to various branches of industry.

I say “comparatively new” because the underlying principles involved in the experiments referred to have, to a certain extent, been employed (in, however, a somewhat restricted sense) for purposes analogous to those that form the basis of this communication.

As indicated by the title, the subject that will now occupy our attention is the use of the electric current as a means of increasing and varying the frictional adhesion of rolling contacts and other rubbing surfaces, and it is proposed to show how this effect may be produced, both by means of the direct action of the current itself and by its indirect action through the agency of electro-magnetism.

Probably the first instance in which the electric current was directly employed to vary the amount of friction between two rubbing surfaces was exemplified in Edison’s electro-motograph, in which the variations in the strength of a telephonic current caused corresponding variations in friction between a revolving cylinder of moistened chalk and the free end of an adjustable contact arm whose opposite extremity was attached to the diaphragm of the receiving telephone.  This device was extremely sensitive to the least changes in current strength, and if it were not for the complication introduced by the revolving cylinder, it is very likely that it would to-day be more generally used.